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Planar laser-induced fluorescence (PLIF) is a crucial spectroscopic technique for measuring minor species [e.g., hydroxyl (OH), methylene (CH), and nitric oxide (NO) radicals] in combustion research, owing to its non-intrusive nature and high sensitivity. However, laser energy attenuation due to absorption poses significant challenges to its application under high-pressure conditions, which may cause asymmetric image intensity distribution along the light propagation direction. An absorption correction method for OH PLIF based on the concept of maximum number density is proposed in the present study. This method offers several key advantages, including simplicity, high accuracy, and versatility, allowing for correcting both time-averaged and instantaneous OH PLIF images. OH PLIF data obtained from a centrally staged combustor at elevated pressures (i.e., 0.3, 0.6, and 1.0 MPa) are utilized to validate the method. Correction for the time-averaged PLIF images achieves a much more symmetric distribution of OH, revealing the overall flame structures that would not have been completely visualized from the original images. The fronts of the pilot and main stage flames have also been recovered from the corrected instantaneous images. This correction algorithm provides an effective way of enhancing data quality for high-cost OH PLIF measurements at pressurized conditions. [ABSTRACT FROM AUTHOR]

Infrared (IR) action spectroscopy is utilized to characterize carbon-centered hydroperoxy-cyclohexyl radicals (·QOOH) transiently formed in cyclohexane oxidation. The oxidation pathway leads to three nearly degenerate ·QOOH isomers, β-, γ-, and δ-QOOH, which are generated in the laboratory by H-atom abstraction from the corresponding ring sites of the cyclohexyl hydroperoxide (CHHP) precursor. The IR spectral features of jet-cooled and stabilized ·QOOH radicals are observed from 3590 to 7010 cm−1 (∼10–20 kcal mol−1) at energies in the vicinity of the transition state (TS) barrier leading to OH radicals that are detected by ultraviolet laser-induced fluorescence. The experimental approach affords selective detection of β-QOOH, arising from its significantly lower TS barrier to OH products compared to γ and δ isomers, which results in rapid unimolecular decay and near unity branching to OH products. The observed IR spectrum of β-QOOH includes fundamental and overtone OH stretch transitions, overtone CH stretch transitions, and combination bands involving OH or CH stretch with lower frequency modes. The assignment of β-QOOH spectral features is guided by anharmonic frequencies and intensities computed using second-order vibrational perturbation theory. The overtone OH stretch (2νOH) of β-QOOH is shifted only a few wavenumbers from that observed for the CHHP precursor, yet they are readily distinguished by their prompt vs slow dissociation rates to OH products. [ABSTRACT FROM AUTHOR]

We report the two-photon absorption laser-induced fluorescence rotational spectrum of the CO B 1Σ+ ← X 1Σ+ Hopfield–Birge system (v′ = 0, v″ = 0) Q-branch in an ∼4850 K, atmospheric pressure plasma torch plume at thermal equilibrium in both the quenching-dominated (low laser intensity) and photoionization-dominated (high laser intensity) regimes. We provide a detailed analysis of the photophysics in these two regimes using a rate equation approach and propose modeling considerations for them as well. In the experimental spectra, distinct rotational transitions up to J″ = 83 are observed, allowing analysis over a very large range of rotational states. Evidence of predissociation is observed for J′ ≥ 64 and is likely due to the interaction with the D′1Σ+ electronic state, which has been proposed in the literature but never observed in the v′ = 0 state. The line positions of higher rotational states show disagreement with line positions calculated from molecular constants in the available literature, suggesting the need for modifications to the constants, which are reported here. A shift in the B 1Σ+ ← X 1Σ+ absorption spectrum toward higher two-photon energy as a result of the second-order Stark shift was observed in the photoionization-dominated spectrum, and the second-order Stark shift cross section was estimated to be 7 ± 3 × 10−18 cm2. The mean photoionization cross section of the excited upper state was inferred by comparing the line broadening of the two spectra and was estimated to be 11 ± 7 × 10−18 cm2. In addition, weak J′-dependent variations of the photoionization cross section were observed and are reported here. [ABSTRACT FROM AUTHOR]

The contribution of atomic nitrogen is fairly possible in plasma-assisted catalytic synthesis of ammonia since it has high adsorption probabilities on solid surfaces. On the other hand, recently, the contribution of vibrational excited molecular nitrogen to ammonia synthesis has been discussed. In this work, we compared the fluxes of atomic nitrogen and vibrational excited molecular nitrogen with the rate of plasma-assisted ammonia synthesis. We employed an atmospheric-pressure nitrogen plasma jet, and the spatial afterglow of the plasma jet and a hydrogen flow irradiated the surface of a ruthenium catalyst. The fluxes of atomic nitrogen and vibrational excited molecular nitrogen were measured by two-photon absorption laser-induced fluorescence spectroscopy and laser Raman scattering, respectively. The synthesis rate of ammonia had a positive correlation with the flux of vibrational excited molecular nitrogen, while the variation of the synthesis rate with the gas flow rate was opposite to the flux of atomic nitrogen. The experimental results indicate the contribution of vibrational excited molecular nitrogen to the synthesis of ammonia using the atmospheric-pressure plasma, where the flux of vibrational excited molecular nitrogen is more than four orders of magnitude higher than that of atomic nitrogen. [ABSTRACT FROM AUTHOR]

An IR–vacuum ultraviolet (VUV) ion-dip spectroscopy method is utilized to examine the IR spectrum of acetaldehyde oxide (CH3CHOO) in the overtone CH stretch (2νCH) spectral region. IR activation creates a depletion of the ground state population that reduces the VUV photoionization signal on the parent mass channel. IR activation of the more stable and populated syn-CH3CHOO conformer results in rapid unimolecular decay to OH + vinoxy products and makes the most significant contribution to the observed spectrum. The resultant IR–VUV ion-dip spectrum of CH3CHOO is similar to that obtained previously for syn-CH3CHOO using IR action spectroscopy with UV laser-induced fluorescence detection of OH products. The prominent IR features at 5984 and 6081 cm−1 are also observed using UV + VUV photoionization of OH products. Complementary theoretical calculations utilizing a general implementation of second-order vibrational perturbation theory provide new insights on the vibrational transitions that give rise to the experimental spectrum in the overtone CH stretch region. The introduction of physically motivated small shifts of the harmonic frequencies yields remarkably improved agreement between experiment and theory in the overtone CH stretch region. The prominent features are assigned as highly mixed states with contributions from two quanta of CH stretch and/or a combination of CH stretch with an overtone in mode 4. The generality of this approach is demonstrated by applying it to three different levels of electronic structure theory/basis sets, all of which provide spectra that are virtually indistinguishable despite showing large deviations prior to introducing the shifts to the harmonic frequencies. [ABSTRACT FROM AUTHOR]

This study was focused on the photochemistry of OAlOH and three possible pathways, which were studied with high-level multireference configuration interaction ab initio calculations. We computed cuts of the six-dimensional potential energy surfaces for the ground, the lowest singlet and triplet excited states, and probed the photodissociation mechanisms and the stabilities. The OAlOH electronic spectrum, with an energy reaching 7.15 eV, contained four prominent peaks. Photodissociation to AlO, OH, and AlOH constituted a plausible mechanism within the deep-UV range (λ = 250.4 nm). Our data indicated the photostability of OAlOH in the near-UV‒Vis region, so detection with laser-induced fluorescence is possible. Fluorescence and phosphorescence may occur upon excitation at 363.5 nm. The roles of OAlOH in the photochemical reactions of Al-bearing molecules in the upper atmosphere and VY Canis Majoris are discussed. [ABSTRACT FROM AUTHOR]

A femtosecond laser induced photofragmentation fluorescence (fs-LIPF) scheme for the sensitive detection and imaging of water vapor is presented. Two photons of 244.3 nm excite water to the D ̃ state and produce hydroxyl radicals in the fluorescing A ̃ state. Two more photons promote electrons from the D ̃ state to a neutral Rydberg state of the (1b2)−1 ionic core through a 2 + 2 doubly resonant process. The resulting high-lying Rydberg state undergoes neutral dissociation, and the energetic hydrogen fragments are detected from their Balmer series fluorescence. These channels (in the low-pressure limit) have detection sensitivities around 1012 molecules per cubic centimeters, orders of magnitude more sensitive than laser-induced fluorescence based approaches, allowing for sensitive non-invasive detection and imaging of water density for many important processes. [ABSTRACT FROM AUTHOR]

Rotationally resolved Fourier-transform spectra of laser-induced fluorescence A 1 Σ u + ∼ b 3 Π u → X 1 Σ g + of K2 molecules were recorded and analyzed, yielding 4053 term values of the spin–orbit (SO) coupled A ∼ b complex of the 39K2 isotopologue with ∼0.01 cm−1 accuracy. Their compilation with 1739 term values from previously published sources allowed them to cover the energy range [9955, 17 436] cm−1 from the bottom of the lower-lying b3Πu state up to the vicinity of the atomic asymptote 4 s 2 S 1 2 + 4 p 2 P 1 2 , with a rotational quantum number J ∈ [0, 149]. The experimental data were processed by a direct 6 × 6 coupled-channel (CC) deperturbation treatment, which accounted explicitly for both SO and electronic-rotational interactions between all six e-symmetry states: A 1 Σ u + ( 0 u + ), b3Πu( 0 u + , 1 u , 2 u ), c3Σu(1u), and B1Πu(1u). The initial parameters of the global deperturbation model have been estimated in the framework of ab initio electronic structure calculations applying multi-reference configuration-interaction and coupled-clusters methods. The interatomic potentials analytically defined for A and b states, as well as SO-splitting of the triplet b state and A ∼ b SO-coupling functions, have been particularly refined to fit the 5792 term values of the 39K2 isotopologue, whereas the rest parameters were fixed on their ab initio values. The resulting mass-invariant parameters of the 6 × 6 CC model reproduced the overall rovibronic term energies of the A ∼ b complex of 39K2 with accuracy, which is well within the experimental errors. The quality of the deperturbation analysis was independently confirmed by comparison with the present obtained 705 and 14 term values of respective 39K41K and 41K2 isotopologues, as well as by agreement between measured and predicted relative intensity distributions in long A ∼ b → X(vX) band progressions. This deperturbation analysis provided the refined dissociation energy Tdis = 17 474.569(5) cm−1 and the long-range coefficient C 3 Σ = 5.501(4) × 105 cm−1 Å3 relevant to the non-relativistic atomic limit 4s + 4p. The derived Tdis yielded the accurate well depth De = 4450.910(5) cm−1 for the ground X 1 Σ g + state, whereas the new C 3 Σ value yielded the improved estimates for atomic K(4 p 2 P 1 2 ; 3 2 ) radiative lifetimes, τ 1 2 = 26.67(3) and τ 3 2 = 26.32(3) ns. [ABSTRACT FROM AUTHOR]

A π-type hydrogen bonding between the OH group and the π electron is a crucial factor for the conformational preference of the molecular structure with a flexible group. However, the information on the effect of the substituent on the OH/π interaction is insufficient. The laser-induced fluorescence (LIF) excitation, the dispersed fluorescence (DF), the IR–UV hole-burning, and the IR dip spectra of jet-cooled 2-(4-methoxyphenyl)ethanol were measured for the first time. Almost all bands observed in the spectral region of 35 550–36 500 cm−1 in the LIF excitation spectrum were successfully assigned with the DF and the IR–UV hole-burning spectra coupled with the quantum chemical calculation at M06-2x/6-311G and MP2/6-311G levels. Five conformers were found in the LIF excitation spectrum. The most stable conformer was Ggπ, and the second most stable conformer was Ggπ′ (the trans rotamer of the methoxy group for Ggπ). Ggπ and Ggπ′ had the OH group directed toward the π electron system of the benzene ring. The OH stretching frequency of Ggπ/Ggπ′ of MPE in the IR dip spectra was red-shifted against that of Ggπ of phenylethanol, indicating that the introduction of the methoxy group would enhance the intramolecular OH/π interaction. In addition, the torsional vibration between the benzene ring and the side chain (−CH2CH2OH) (mode 63) was observed in the DF spectra of the Ggπ–00 and Ggπ′–00 band excitation, but their intensities were rather different, resulting from the different orientation of the OH group for each conformer toward the π electron system. The methoxy group would increase the negative charge on the benzene ring and would enhance the intramolecular OH/π interaction through the electrostatic interaction. [ABSTRACT FROM AUTHOR]

GaCH2, a free radical thought to play a role in the chemical vapor deposition of gallium-containing thin films and semiconductors, has been spectroscopically detected for the first time. The radical was produced in a pulsed discharge jet using a precursor mixture of trimethylgallium vapor in high pressure argon and studied by laser-induced fluorescence and wavelength resolved emission techniques. Partially rotationally resolved spectra of the hydrogenated and deuterated species were obtained, and they exhibit the nuclear statistical weight variations and subband structure expected for a 2A2–2B1 electronic transition. The measured spectroscopic quantities have been compared to our own ab initio calculations of the ground and excited state properties. The electronic spectrum of gallium methylene is similar to the corresponding spectrum of the aluminum methylene radical, which we reported in 2022. [ABSTRACT FROM AUTHOR]

In pursuit of diamond nanoparticles, a capacitively-coupled radio frequency flow-through plasma reactor was operated with methane-argon gas mixtures. Signatures of the final product obtained microscopically and spectroscopically indicated that the product was an amorphous form of graphite. This result was consistent irrespective of combinations of the macroscopic reactor settings. To explain the observed synthesis output, measurements of C2 and gas properties were carried out by laser-induced fluorescence and optical emission spectroscopy. Strikingly, the results indicated a strong gas temperature gradient of 100 K per mm from the center of the reactor to the wall. Based on additional plasma imaging, a model of hot constricted region (filamentation region) was then formulated. It illustrated that, while the hot constricted region was present, the bulk of the gas was not hot enough to facilitate diamond sp 3 formation: characterized by much lower reaction rates, when compared to sp 2, sp 3 formation kinetics are expected to become exponentially slow. This result was further confirmed by experiments under identical conditions but with a H2/CH4 mixture, where no output material was detected: if graphitic sp 2 formation was expected as the main output material from the methane feedstock, atomic hydrogen would then be expected to etch it away in situ, such that the net production of that sp 2-hybridized solid material is nearly a zero. Finally, the crucial importance of gas heating was corroborated by replacing RF with microwave source whereby facile sp 3 production was attained with H2/CH4 gas mixture. [ABSTRACT FROM AUTHOR]

In response to the deficiencies of traditional power transformer fault detection techniques, such as low sensitivity and the inability for online monitoring, a novel transformer fault diagnosis model combining laser-induced fluorescence (LIF) technology with deep learning is proposed. Initially, the spectral data of transformer insulation oil is acquired using LIF technology, yielding spectral data for various fault types. Subsequently, MinMaxScaler and standard normalized variate methods are employed for denoising and preprocessing the spectral data. The preprocessed data is then subjected to dimensionality reduction using linear discriminant analysis and T-distributed stochastic neighbor embedding to ensure that the spectral data retains maximal feature information while minimizing its dimensionality. Following this, long short-term memory, bidirectional long short-term memory (BiLSTM), dung beetle optimizer-BiLSTM, convolutional neural network, and support vector machine models are constructed. The reduced-dimensional data is fed into each of the five models for training to facilitate transformer fault diagnosis. Through comparative analysis among the five models, the optimal model is selected. Experimental results indicate that the dung beetle optimization-BiLSTM model is the most suitable for transformer fault diagnosis in this experiment, underscoring its significant implications for ensuring the safety of power systems. [ABSTRACT FROM AUTHOR]

Blowoff limits are essential in establishing the combustor operating envelope. Hence, there is a great demand for practical aero-engines to extend the blowoff limits further. In this work, the behavior of non-premixed swirling flames under fuel flow rate oscillations was investigated experimentally close to its blowoff limits. The methane flame was stabilized on the axisymmetric bluff body and confined in a square quartz enclosure. External acoustic forcing at 400 Hz was applied to the fuel flow to induce a fuel mass flow rate fluctuation (FMFRF) with varying amplitudes. A high-speed burst-mode laser and cameras ran at 20 kHz for OH*-chemiluminescence (CL), CH2O-, and SO2-PLIF measurements, offering the visualization of the two-dimensional flame structure and heat release distribution, temporally and spatially. The results show that the effect of FMFRF is predominantly along the central axis without altering the time-averaged flame structure and blowoff transient. However, the blowoff limits are extended due to the enhanced temperature and longer residence time induced by FMFRF. This work allows us to explore the mechanism of flame instability further. [ABSTRACT FROM AUTHOR]

Recent progress in studies of Rydberg double-well electronic energy states of MeNg (Me = 12-group atom, Ng = noble gas atom) van der Waals (vdW) molecules is presented and analysed. The presentation covers approaches in experimental studies as well as ab initio-calculations of potential energy curves (PECs). The analysis is shown in a broader context of Rydberg states of hetero- and homo-diatomic molecules with PECs possessing complex 'exotic' structure. Laser induced fluorescence (LIF) excitation spectra and dispersed emission spectra employed in the spectroscopical characterization of Rydberg states are presented on the background of the diverse spectroscopic methods for their investigations such as laser vaporization–optical resonance (LV-OR), pump-and-probe methods, and polarization labelling spectroscopy. Important and current state-of-the-art applications of Rydberg states with irregular potentials in photoassociation (PA), vibrational and rotational cooling, molecular clocks, frequency standards, and molecular wave-packet interferometry are highlighted. [ABSTRACT FROM AUTHOR]

In many research fields, the demand for miniaturized laser-induced fluorescence (LIF) detection systems has been increasing. This work has developed a compact LIF detector, employing a laser diode as the excitation source and a photodiode as the photodetector with an adjustable laser focal spot, to meet the diverse requirements of various observation targets, such as capillaries, PCR tubes, and microfluidic chips. It features the functionalities of background fluorescence correction, the adaptive adjustment of the dynamic range, and constant power control for the laser. The influence of the excitation power on the detection limit was studied through experiments, and the configuration results for LED/LD as light sources and 487/450 nm wavelengths were compared and optimized. A fully integrated, compact, modular epifluorescence LIF detector was subsequently constructed, measuring 40 × 22 × 38 mm3 in total size, with a cost of USD 320, and achieving a detection limit of 0.4 nM for fluorescein sodium. Finally, the detector was integrated into a nucleic acid detection system with a microfluidic chip on the Chinese Space Station (CSS) and was also tested with PCR tubes and capillaries, proving its broad practicality and adaptability to various analytical systems. [ABSTRACT FROM AUTHOR]

In this study, we designed three promising platforms based on metal–organic frameworks (MOFs) to develop paper-based analytical devices (PADs) for biosensing applications. PADs have become increasingly popular in field sensing in recent years due to their portability, low cost, simplicity, efficiency, fast detection capability, excellent sensitivity, and selectivity. In addition, MOFs are excellent choices for developing highly sensitive and selective sensors due their versatility for functionalizing, structural stability, and capability to adsorb and desorb specific molecules by reversible interactions. These materials also offer the possibility to modify their structure and properties, making them highly versatile and adaptable to different environments and sensing needs. In this research, we synthesized and characterized three different amino-functionalized MOFs: UiO-66-NH2 (Zr), MIL-125-NH2 (Ti), and MIL-101-NH2 (Fe). These MOFs were used to fabricate PADs capable of sensitive and portable monitoring of alkaline phosphatase (ALP) enzyme activity by laser-induced fluorescence (LIF). Overall, amino-derivated MOF platforms demonstrate significant potential for integration into biosensor PADs, offering key properties that enhance their performance and applicability in analytical chemistry and diagnostics. [ABSTRACT FROM AUTHOR]

Laser-induced fluorescence (LIF) is an established noninvasive measurement method to determine temperature distributions and local gas concentrations in combustion processes with high spatial and temporal resolution. This work presents high-precision LIF spectra of acetone and other tracers at ambient conditions. By using a large UV-sensitive sCMOS camera instead of an image intensified camera, many issues like nonlinearity, varying sensitivity, vignetting, limited resolution etc. could be minimized or eliminated. Particular care was taken to remove residual stray light and to calibrate the spectra with metrological traceability to the International System of Units SI. [ABSTRACT FROM AUTHOR]

In this work, we investigated non-equilibrium plasma produced by nanosecond repetitively pulsed glow discharges applied across a lean premixed methane-air flame. The flame is stationary, axisymmetric, and laminar. The discharges are applied on the symmetry axis crossing the reactant gases, flame front, and product gases, allowing phase-locked averaged measurements and comparisons with axisymmetric numerical simulations. The thermal effect and methyl radical production are quantified in the discharge in the reactant gas region. One-dimensional, two-beam, hybrid, femtosecond-picosecond, coherent anti-Stokes Raman scattering is used to acquire spatial and temporal profiles of temperature and oxygen-to-nitrogen concentration ratio. Photo-fragmentation laser-induced fluorescence is used to acquire quantitative two-dimensional profiles of methyl radicals in the discharge providing the first quantitative imaging of methyl produced ahead of a flame by plasma-induced methane dissociation. The spatial profiles of temperature and oxygen-to-nitrogen concentration ratio are in steady state, indicating that individual discharges have an insignificant heating effect. Upper and lower bounds of the produced mole fraction of methyl radicals in the plasma are obtained due to uncertainties in the collisional quenching rates of excited state methylidyne radicals in the plasma. The discharges produce a maximum of 600–1100 ppm of methyl radicals upstream of the flame front within 25 ns. This amount is similar to the predicted methyl mole fraction for the flame without plasma and thus represents a significant chemical perturbation to the reactants upstream of the flame front. The produced methyl follows an exponential decay in the first microsecond after the discharge with a decay constant of 8 µs close to the flame, and 0.8 µs further from the flame. The decay then deviates from the exponential curve and the methyl persists for tens of microseconds. The results suggest that for the tested configuration, the thermal effect of individual discharges through fast gas heating is negligible, while active chemical species are produced in large quantities in the reactant gases, upstream of the flame front. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental study of the dynamic characteristics of the process of laser fragmentation/laser-induced fluorescence (LF/LIF) of trinitrotoluene traces on a paper surface under synchronized double-pulse laser irradiation. An Nd:YAG-laser (266 nm) was used for the fragmentation of TNT molecules, while fluorescence excitation of their NO fragments was performed using a KrF laser with a generation line of 247.867 nm in the region of the location of the bandhead of the P12 branch of the γ(0, 2) absorption band of the NO molecule. It was shown that the dissociation process of TNT traces has an inertial character and continues after the cessation of the fragmenting laser pulse. It was found that with the delay values between the fragmenting and probing laser pulses in the region of 200 ns, the efficiency of the LF/LIF method can be increased by 12 times. This paper presents the results of an experimental evaluation of the efficiency of two-pulse LF/LIF compared to single-pulse laser exposure, where the fragmentation of TNT molecules and excitation of their NO fragments were simultaneously performed by KrF laser pulses. The possibility of multiple increases in the efficiency of two-pulse LF/LIF with an increase in the energy density of the fragmenting laser radiation was shown. The obtained results are important in terms of increasing the sensitivity and/or range of the LF/LIF method for remote detection of traces of nitrocompounds. [ABSTRACT FROM AUTHOR]

Electroosmotic flow significantly impacts the resolution of separations in capillary electrophoresis and its modification is often necessary. Coating of the inner capillary surface either dynamically or permanently offers a way to alter the electroosmotic flow, potentially reducing the adsorption of analytes, in our case liposomes, to the capillary wall. At first, we measured fluorescently labeled liposomes in an uncoated capillary by capillary electrophoresis with laser-induced fluorescence detection. We used a special procedure of the electrophoretic experiment allowing us to observe the development of peak shape at the early stages of migration. We proved that the liposomes were adsorbed to the capillary wall, which led to a very quick and severe dispersion of their peak during their electromigration. For this reason, we used a commercially coated capillary with polyvinyl alcohol, where at the same separation conditions, we observed the peak of the liposome with a stable shape during the migration. However, this capillary is costly, thus four simple dynamic coating methods were tested for four polymers, namely Pluronic F-127, polyvinyl pyrrolidone K30, polyethylene glycol, and polydiallyldimethylammonium chloride. Among them, we chose a method where we flushed the capillary with a 10% solution of polyvinyl pyrrolidone K30 before the first measurement. In addition, in-house made permanent coating with linear polyacrylamide was investigated, which has led to effective suppression of the electroosmotic flow and stable liposome peak, not dispersed during its migration. Liposome separation using this coating fully confirmed that the studied liposomes are negatively charged and migrate in the anodic direction. [ABSTRACT FROM AUTHOR]

We have analyzed the effects of the spreads in experimental parameters on the reliability of speeds and angular distributions extracted from a generic surface-scattering experiment based on planar laser-induced fluorescence detection. The numerical model assumes a pulsed beam of projectile molecules is directed at a surface. The spatial distribution of the scattered products is detected by imaging the laser-induced fluorescence excited by a thin, pulsed sheet of laser light. Monte Carlo sampling is used to select from realistic distributions of the experimental parameters. The key parameter is found to be the molecular-beam diameter, expressed as a ratio to the measurement distance from the point of impact. Measured angular distributions are negligibly distorted when this ratio is <∼10%. Measured most-probable speeds are more tolerant, being undistorted when it is <∼20%. In contrast, the spread of speeds or of corresponding arrival times in the incident molecular beam has only very minor systematic effects. The thickness of the laser sheet is also unimportant within realistic practical limits. These conclusions are broadly applicable to experiments of this general type. In addition, we have analyzed the specific set of parameters designed to match the experiments on OH scattering from a liquid perfluoropolyether (PFPE) surface in the Paper I [Roman et al., J. Chem. Phys. 158, 244704 (2023)]. This reveals that the detailed form of the molecular-beam profile is important, particularly on apparent angular distributions, for geometric reasons that we explain. Empirical factors have been derived to correct for these effects. [ABSTRACT FROM AUTHOR]

The isoelectronic molecules UN and UO+ are known to have Ω = 3.5 and Ω = 4.5 ground states, respectively (where Ω is the unsigned projection of the electronic angular momentum along the internuclear axis). A ligand field theory model has been proposed to account for the difference [Matthew and Morse, J. Chem. Phys. 138, 184303 (2013)]. The ground state of UO+ arises from the U3+(5f3(4I4.5))O2− configuration. Owing to the higher nominal charge of the N3− ligand, the U3+ ion in UN is stabilized by promoting one of the 5f electrons to the more polarizable 7s orbital, reducing the repulsive interaction with the ligand and rendering U3+(5f27s(4H3.5))N3− the lowest energy configuration. In the present work, we have advanced the characterization of the UN ground state through studies of two electronic transitions, [18.35]4.5-X(1)3.5 and [18.63]4.5-X(1)3.5, using sub-Doppler laser excitation techniques with fluorescence detection. Spectra were recorded under field-free conditions and in the presence of static electric or magnetic fields. The ground state electric dipole moment [μ = 4.30(2) D] and magnetic ge-factor [2.160(9)] were determined from these data. These values were both consistent with the 5f27s configurational assignment. Dispersed fluorescence measurements were used to determine vibrational constants for the ground and first electronically excited states. Electric dipole moments and magnetic ge-factors are also reported for the higher-energy electronically excited states. [ABSTRACT FROM AUTHOR]

Ageing is a complex biological process with variations among individuals, leading to the development of ageing clocks to estimate biological age. Glycans, particularly in immunoglobulin G (IgG), have emerged as potential biomarkers of ageing, with changes in glycosylation patterns correlating with chronological age. For precision analysis, three different plasma pools were analysed over 26 days in tetraplicates, 312 samples in total. In short-term variability analysis, two cohorts were analysed: AstraZeneca MFO cohort of 26 healthy individuals (median age 20) and a cohort of 70 premenopausal Chinese women (median age 22.5) cohort monitored over 3 months. Long-term variability analysis involved two adult men aged 47 and 57, monitored for 5 and 10 years, respectively. Samples were collected every 3 months and 3 weeks, respectively. IgG N-glycan analysis followed a standardized approach by isolating IgG, its subsequent denaturation and deglycosylation followed by glycan cleanup and labelling. Capillary gel electrophoresis with laser-induced fluorescence (CGE-LIF) and ultra-performance liquid chromatography analyses were employed for glycan profiling. Statistical analysis involved normalization, batch correction, and linear mixed models to assess time effects on derived glycan traits. The intermediate precision results consistently exhibited very low coefficient of variation values across all three test samples. This consistent pattern underscores the high level of precision inherent in the CGE method for analysing the glycan clock of ageing. The AstraZeneca MFO cohort did not show any statistically significant trends, whereas the menstrual cycle cohort exhibited statistically significant trends in digalactosylated (G2), agalactosylated (G0) and fucosylation (F). These trends were attributed to the effects of the menstrual cycle. Long-term stability analysis identified enduring age-related trends in both subjects, showing a positive time effect in G0 and bisected N-acetylglucosamine, as well as a negative time effect in G2 and sialylation, aligning with earlier findings. Time effects measured for monogalactosylation, and F remained substantially lower than ones observed for other traits. The study found that IgG N-glycome analysis using CGE-LIF exhibited remarkably high intermediate precision. Moreover, the study highlights the short- and long-term stability of IgG glycome composition, coupled with a notable capacity to adapt and respond to physiological changes and environmental influences such as hormonal changes, disease, and interventions. The discoveries from this study propel personalized medicine forward by deepening our understanding of how IgG glycome relates to age-related health concerns. This study underscores the reliability of glycans as a biomarker for tracking age-related changes and individual health paths. [ABSTRACT FROM AUTHOR]

In this study, we explore the potential of using laser-induced photo-fragmentation of O3 by UV radiation as a quantitative diagnostic tool in non-thermal O2-mixed plasmas. We analyze the optical processes of O3 using a comprehensive kinetic model with a 226 nm laser, which is typically used in the two-photon absorption laser-induced fluorescence (TALIF) measurement of O atoms. Our model demonstrates that the fluorescence intensity from atomic O fragments produced by the same laser is directly proportional to the population of precursor O3. This makes various diagnostic purposes achievable through the proposed O3 full photo-fragmentation (FPF) TALIF spectroscopy, including calibration of TALIF signals of O atoms and quantification of both O and O3 in O2-mixed plasmas. We present detailed theoretical principles, technical requirements, and successful examples of implementation for different diagnostic aims using the proposed O3 FPF-TALIF spectroscopy. However, we also specify the limitations of the developed diagnostic methods, particularly under low E/N conditions (<30 Td), where other interferential species such as the vibrationally excited ground-state O 2 ( X 3 Σ g − , v ≠ 0) are abundantly produced. [ABSTRACT FROM AUTHOR]

We present the first experimental application of coherent Raman spectroscopy (CRS) on the ro-vibrational ν2 mode spectrum of methane (CH4). Ultrabroadband femtosecond/picosecond (fs/ps) CRS is performed in the molecular fingerprint region from 1100 to 2000 cm−1, employing fs laser-induced filamentation as the supercontinuum generation mechanism to provide the ultrabroadband excitation pulses. We introduce a time-domain model of the CH4ν2 CRS spectrum, including all five ro-vibrational branches allowed by the selection rules Δv = 1, ΔJ = 0, ±1, ±2; the model includes collisional linewidths, computed according to a modified exponential gap scaling law and validated experimentally. The use of ultrabroadband CRS for in situ monitoring of the CH4 chemistry is demonstrated in a laboratory CH4/air diffusion flame: CRS measurements in the fingerprint region, performed across the laminar flame front, allow the simultaneous detection of molecular oxygen (O2), carbon dioxide (CO2), and molecular hydrogen (H2), along with CH4. Fundamental physicochemical processes, such as H2 production via CH4 pyrolysis, are observed through the Raman spectra of these chemical species. In addition, we demonstrate ro-vibrational CH4v2 CRS thermometry, and we validate it against CO2 CRS measurements. The present technique offers an interesting diagnostics approach to in situ measurement of CH4-rich environments, e.g., in plasma reactors for CH4 pyrolysis and H2 production. [ABSTRACT FROM AUTHOR]

Gangliosides are sialic acid-containing glycosphingolipids that play an essential role in many biological and pathophysiological processes. They are present in high amounts in the central nervous system and their abnormal metabolism or expression has been observed in many diseases. We have developed and validated a sensitive capillary electrophoresis laser-induced fluorescence (CE-LIF) method for the separation and quantification of oligosaccharides digested from nine gangliosides of high biological relevance. APTS was used for the labeling of the glycans. Reverse polarity CE was performed for the separation of the labeled glycans bearing negative charges. The optimized background electrolyte is a 15 mM lithium acetate buffer with pH of 5 containing 5% w/v linear polyacrylamide, which allows for the separation of all nine gangliosides. Validation parameters including linearity, precision, and accuracy were evaluated. LOQ and LOD were in the nM range, comparable to those of LC-MS techniques. The method was used to identify and quantify the ganglioside pattern of glioblastoma and neuroblastoma cell lines. The presented method is a valuable tool for further investigations aiming at understanding the role of gangliosides in various neurological diseases or CNS tumors. [ABSTRACT FROM AUTHOR]

One of the important choices for achieving decarbonization goals on a large scale is the extensive use of H 2. However, the highly reactive nature of H 2 often leads to challenges such as flashback, excessive NO x emissions, and combustion instability when traditional combustion methods are directly applied. Therefore, developing safe and efficient H 2 combustion technologies are currently important research directions in gas combustion. It holds significant importance for addressing the coordinated development of future energy and the environment. In recent years, hydrogen-enriched methane has been widely applied in gas turbines with the aim of reducing carbon emissions. Ammonia is also regarded as an important carrier of hydrogen. The blending of ammonia with hydrogen has been widely recognized and accepted for simultaneous use. The use of H 2 O as a diluent is another technology capable of achieving stable H 2 combustion and reducing NO x emissions. Syngas, primarily composed of CO and H 2 , serves as the main fuel for Integrated Gasification Combined Cycle technology. These are collectively referred to as hydrogen hybrid fuels, and their combustion chemical properties are all influenced by hydrogen. In recent years, significant efforts have been made to deepen the understanding of flame structures of pure hydrogen and these hydrogen hybrid fuels through advanced numerical simulations and experimental diagnostics. The utilization of Planar Laser Induced Fluorescence techniques for flame structure characterization has significantly advanced the understanding of flame-flow-acoustic coupling mechanisms in phenomena such as flashback processes, NO x emission mechanisms, and combustion instability. This has also contributed to the development and validation of advanced numerical models. This paper categorizes hydrogen and various hydrogen hybrid fuels according to different combustion application scenarios and purposes. It discusses the application of Planar Laser Induced Fluorescence technology in flashback, NO x emissions, and combustion instability aspects across different hydrogen hybrid fuels. This brief review aims to provide useful references for researchers and engineers designing and conducting foundational experiments on flame structures and combustion instability of hydrogen and hydrogen hybrid fuels. • Thoroughly summarize the applications of PLIF in studying the combustion characteristics of hydrogen fuel. • Provide insights into the application of laser diagnostic in the field of turbulent combustion of hydrogen fuels. • A detailed discussion is provided on the complex flow-flame interactions in unstable combustion of hydrogen fuel. [ABSTRACT FROM AUTHOR]

The formation and transportation of short-lived species on/within the plasma-liquid interfacial layer plays a crucial role in various applications because of their high chemical reactivity. However, the experimental detection and quantification of these short-lived species, such as ˙OH radicals, at the gas–liquid interface still pose formidable challenges. This study confronts this challenge by employing incident microscopic laser-induced fluorescence (mLIF) method to capture the OH-LIF signals on the interfacial layer at different time moments of the post-discharge phase under high spatial resolution. The temporal evolution of ˙OH density is subsequently quantified by fitting the OH-LIF decay behavior to a reaction-dissolution model. Results reveal that increasing the pulse width serves better to enhance ˙OH generation on liquid surface, reaching a density of 1.25 × 1016 cm−3. Furthermore, the cathode-solution interface demonstrates significantly enhanced ˙OH production compared to the anode-solution interface. These results underscore the efficacy of incident mLIF in quantitatively probing short-lived ˙OH-radical production at the interfacial layer in pulsed-driven plasma-solution interactions, with potential applicability to other reactive species. [ABSTRACT FROM AUTHOR]

Mine water inrush disaster can quickly cause significant economic losses and casualties because of its strong concealing and rapid burst speed. Quickly identifying the source of mine water inrush is of great practical significance. Compared with the traditional hydrochemical analysis method, the laser-induced fluorescence (LIF) technology has fast reaction speed, high sensitivity, and strong stability, which makes up for the shortcomings of the traditional method. As an integrated algorithm, random forest (RF) has the advantage of high accuracy. A combination of LIF technology and RF algorithm is proposed to identify mine water inrush source rapidly. The experimental samples were collected from a coal mine in Hainan City, Anhui Province, and a total of 525 sets of water samples to be tested for experiments by mixing goaf water and sandstone water into A-G7 species according to different proportions. Moving average smoothing (MA), Savitzky-Golay Smoothing (SG), First derivative (FD), and Second derivative (SD) methods are used to preprocess the original spectral data to reduce the noise and interference information existing in the original spectral data. By comparison, the Moving average smoothing (MA) method has high classification accuracy and is the final method for noise reduction. Then, the RF algorithm is used to delete the less critical spectrum after noise reduction and select the characteristic wavelength with the minimum classification error of 0. Finally, SVM, PCA-SVM, MA-SVM, MA-PCA-SVM, and MA-RF algorithm recognition models were established, respectively. Comparing the prediction accuracy of the test set, the accuracy of the MA-RF algorithm in the five groups of models reached 100%, which can quickly and accurately predict mine water inrush. [ABSTRACT FROM AUTHOR]

Copper oxide nanoparticles (CuONPs) have been produced on a large scale because they can be applied across various fields, especially in nano-enabled healthcare and agricultural products. However, the increasing use of CuONPs leads to their release and accumulation into the environment. The CuONPs uptaken by seeds and their implications on germination behavior have been reported, but little is known or understood about their impact on photosynthesis in seed tissues. To fill knowledge gaps, this study evaluated the effects of CuONP concentrations (0–300 mg L−1) on the photosynthetic activity of Inga laurina seeds. The microscopy data showed that CuONPs had an average size distribution of 57.5 ± 0.7 nm. Copper ion release and production of reactive oxygen species (ROS) by CuONPs were also evaluated by dialysis and spectroscopy experiments, respectively. CuONPs were not able to intrinsically generate ROS and released a low content of Cu2⁺ ions (4.5%, w/w). Time evolution of chlorophyll fluorescence imaging and laser-induced fluorescence spectroscopy were used to monitor the seeds subjected to nanoparticles during 168 h. The data demonstrate that CuONPs affected the steady-state maximum chlorophyll fluorescence ( F m ′ ), the photochemical efficiency of photosystem II ( F v / F m ), and non-photochemical quenching (NPQ ) of Inga laurina seeds over time. Besides, the NPQ significantly increased at the seed development stage, near the root protrusion stage, probably due to energy dissipation at this germination step. Additionally, the results indicated that CuONPs can change the oscillatory rhythms of energy dissipation of the seeds, disturbing the circadian clock. In conclusion, the results indicate that CuONPs can affect the photosynthetic behavior of I. laurina seeds. These findings open opportunities for using chlorophyll fluorescence as a non-destructive tool to evaluate nanoparticle impact on photosynthetic activity in seed tissues. [ABSTRACT FROM AUTHOR]

The kinetic study of the gas-phase reactions of hydroxyl (OH) radicals and chlorine (Cl) atoms with CF3CHFCF2OCH3 (HFE-356mec3) and CHF2CHFOCF3 (HFE-236ea1) was performed by the pulsed laser photolysis/laser-induced fluorescence technique and a relative method by using Fourier Transform infrared (FTIR) spectroscopy as detection technique. The temperature dependences of the OH-rate coefficients (kOH(T) in cm3s−1) between 263 and 353 K are well described by the following expressions: 9.93 × 10–13exp{-(988 ± 35)/T}for HFE-356mec3 and 4.75 × 10−13exp{-(1285 ± 22)/T} for HFE-236ea1. Under NOx-free conditions, the rate coefficients kCl at 298 K and 1013 mbar (760 Torr) of air were determined to be (2.30 ± 1.08) × 10–13 cm3s−1and (1.19 ± 0.10) × 10–15 cm3s–1, for HFE-356mec3 and HFE-236ea1, respectively. Additionally, the relative kinetic study of the Cl + CH2ClCHCl2 reaction was investigated at 298 K, as it was used as a reference reaction in the kinetic study of the Cl-reaction with HFE-356mec3 and discrepant rate coefficients were found in the literature. The global atmospheric lifetimes were estimated relative to CH3CCl3 at the tropospheric mean temperature (272 K) as 1.4 and 8.6 years for HFE-356mec3 and HFE-236ea1, respectively. These values combined with the radiative efficiencies for HFE-356mec3 and HFE-236ea1 derived from the measured IR absorption cross sections (0.27 and 0.41 W m−2 ppv−1) yield global warming potentials at a 100-yrs time horizon of 143 and 1473, respectively. The contribution of HFE-356mec3 and HFE-236ea1 to global warming of the atmosphere would be large if they become widespread increasing their atmospheric concentration. [ABSTRACT FROM AUTHOR]

An experiment was carried out using a scale model of a tall building, with the goal of investigating the role of individual buildings in the dispersion of air pollution. Pollutant dispersion around an isolated building with a height-to-length aspect ratio of 1.4 is investigated using simultaneous particle image velocimetry and planar laser induced fluorescence. Dye is released from a ground-level point source five building heights upstream of the tall building. It was found that in this case the scalar plume was dispersed laterally strongly by the building, but only slightly vertically. It is hypothesized that this is due to 94% of the plume impinging below the stagnation point on the front of the building and being drawn into the horseshoe vortex. We expect this fraction would be lower in a case in which the building is in an array of smaller buildings, and that this would lead to more vertical dispersion. [ABSTRACT FROM AUTHOR]

The small signal-to-noise ratio (SNR) of conventional laser induced fluorescence (LIF) measurements using a continuous wave laser, either diode or dye, is typically overcome by amplitude modulating the laser at a specific frequency and then using lock-in amplification to extract the signal from measurement noise. Here, we present LIF measurements of the neutral helium velocity distribution function in an rf plasma using frequency modulated (FM) laser injection. A pulse train of 100% amplitude modulation is generated synthetically with a random sequence of pulse lengths. The FM signal then drives an acoustic optic modulator placed in the path of the injection beam in an LIF measurement. The signal from a fast photomultiplier tube is digitized and cross-correlated with the known modulation signal. The resultant FM-based LIF signal outperforms a conventional lock-in-based LIF measurement on the same plasma in terms of SNR and precision. [ABSTRACT FROM AUTHOR]

Electric motors with high-power densities are required for the implementation of electromobility. To achieve this, direct liquid cooling methods are increasingly being considered, in which oil is injected into the motor compartment. This results in a two-phase flow that can be used for efficient cooling. However, the oil, which can also penetrate the air gap between the rotor and stator, can also lead to additional losses due to increased friction. Since little is known about the two-phase flow in such systems, especially in the air gap, it is investigated by means of simple optical visualizations and high-speed laser-induced fluorescence imaging as well as torque measurements. The measurements are carried out in the air gap of an optically accessible generic model of a directly cooled electric motor. Speed variations were performed from 100 to 2000 rpm, and three different two-phase flow regimes were observed. At low speeds (Flow Regime 1), the air gap is filled locally with oil in radial direction, in the medium speed range (Flow Regime 2) with foam, while at high speeds (Flow Regime 3) separated films were observed on the rotor and stator. The torque difference between the two-phase and single-phase operation, which quantifies the mechanical losses due to the injected oil, increased continuously due to the oil in the air gap until it reached a maximum in Flow Regime 2 due to foam formation. In Flow Regime 3, the torque difference was negative. This was attributed to the fact that the grooves in the stator were filled with oil, thus reducing the turbulence generation of the air flow. [ABSTRACT FROM AUTHOR]

The azimuthal dynamics of ions along the inner pole of a Hall thruster with a centrally mounted cathode and a magnetic shielding topography are experimentally investigated. A time-averaged laser-induced fluorescence diagnostic is implemented to characterize the azimuthal ion velocity distribution, and its moments are computed numerically to infer bulk rotation speed and ion temperature. It is found that the time-averaged ion swirl velocity grows to 2 km/s in the near-pole region, and the cathode ions exhibit ion temperatures in the azimuthal direction approaching 8 eV. Both of these quantities exceed the speeds and temperatures anticipated from classical acceleration and heating. Time-resolved laser-induced fluorescence is then employed to investigate the role of plasma fluctuations in driving the time-averaged ion properties. Semicoherent fluctuations at 90 kHz are observed in the ion velocity distribution and its associated moments. These oscillations are correlated with the gradient-driven anti-drift wave, which propagates azimuthally in the near-field cathode plume. Quasilinear theory is used to construct a 1D model for acceleration and heating of the ion population as a result of the anti-drift mode. This approach demonstrates qualitative agreement with the time-averaged ion velocity and temperature, suggesting that the anti-drift mode may be a dominant driver of azimuthal ion acceleration and heating in front of the cathode keeper and the inner half of the inner front pole cover. These results are discussed in terms of their relevance to the erosion of thruster surfaces in the near-field cathode plume. [ABSTRACT FROM AUTHOR]

Chlorophyll has long been used as a natural indicator of plant health and photosynthetic efficiency. Laser-induced fluorescence (LIF) is an emerging technique for understanding broad spectrum organic processes and has more recently been used to monitor chlorophyll response in plants. Previous work has focused on developing a LIF technique for imaging moss mats to identify metal contamination with the current focus shifting toward application to moss fronds and aiding sample collection for chemical analysis. Two laser systems (CoCoBi a Nd:YGa pulsed laser system and Chl-SL with two blue continuous semiconductor diodes) were used to collect images of moss fronds exposed to increasing levels of Cu (1, 10, and 100 nmol/cm2) using a CMOS camera. The best methods for the preprocessing of images were conducted before the analysis of fluorescence signatures were compared to a control. The Chl-SL system performed better than the CoCoBi, with dynamic time warping (DTW) proving the most effective for image analysis. Manual thresholding to remove lower decimal code values improved the data distributions and proved whether using one or two fronds in an image was more advantageous. A higher DTW difference from the control correlated to lower chlorophyll a/b ratios and a higher metal content, indicating that LIF, with the aid of image processing, can be an effective technique for identifying Cu contamination shortly after an event. [ABSTRACT FROM AUTHOR]

The problems of laser-induced fluorescence (LIF) measurements in a partially saturated regime with spatially dependent laser intensity in the sample (caused by absorption) are analyzed. The obtained equations are tested by means of LIF of free tellurium atoms in a plasma of an atmospheric pressure dielectric barrier discharge (DBD) by comparing fluorescence and absorption measurements. The results show a high reliability of LIF measurements. [ABSTRACT FROM AUTHOR]

Cool red giant stars exhibit absorption bands of calcium monochloride (CaCl) in the optical region. In this work, the bands of CaCl corresponding to the A2Π − X2Σ+ transition with v ′ ≤ 4 and v ″ ≤ 4, and B2Σ+ − X2Σ+ transition with v ′ ≤ 2 and v ″ ≤ 2 are rotationally analyzed with PGOPHER, a multipurpose program for simulating and fitting molecular spectra. All bands were analyzed using high-resolution absorption spectra collected at the National Solar Observatory in 1985, calibrated with atomic lines from a high-resolution emission spectrum obtained in a separate hollow cathode experiment. The results are compared with previous laser-induced fluorescence measurements. Overall, the accuracy of spectroscopic constants for the A2Π and B2Σ+ states is improved. Scaled transition dipole moment calculations were used to obtain line strengths. Line lists are provided with Einstein A coefficients and oscillator strengths, which can be used to determine CaCl stellar abundances. Additionally, isotope splittings allowed us to estimate band origins for the 40Ca37Cl isotopologue based on band-head positions. [ABSTRACT FROM AUTHOR]

Laser-induced fluorescence (LIF) Doppler spectroscopy using an optical vortex beam with an asymmetric intensity distribution, referred to as aOVLIF, is proposed as a new method to measure plasma flow velocity. LIF spectra were calculated numerically using typical laboratory low-temperature plasma parameters, and it was revealed that an ion flow across the beam produces a frequency shift of the spectra. This method also has the capability of temperature measurements. The propagation effects of asymmetric optical vortex beams are discussed assuming an actual experiment, and it is found that the sensitivity to the transverse flow velocity is approximately unchanged. The aOVLIF method, which exploits the inhomogeneous phase structure of optical vortices, can be applied to the determination of three-dimensional velocity vectors and promises to enhance the usefulness of conventional LIF spectroscopy using plane waves. [ABSTRACT FROM AUTHOR]

Single‐molecule localization microscopy (SMLM) has revolutionized optical microscopy by exceeding the diffraction limit and revealing previously unattainable nanoscale details of cellular structures and molecular dynamics. This super‐resolution imaging capability relies on fluorophore photoswitching, which is crucial for optimizing the imaging conditions and accurately determining the fluorophore positions. To understand the general on and off photoswitching mechanisms of single dye molecules, various photoswitching reagents were evaluated. Systematic measurement of the single‐molecule‐level fluorescence on and off rates (kon and koff) in the presence of various photoswitching reagents and theoretical calculation of the structure of the photoswitching reagent‐fluorophore pair indicated that the switch‐off mechanism is mainly determined by the nucleophilicity of the photoswitching reagent, and the switch‐on mechanism is a two‐photon‐induced dissociation process, which is related to the power of the illuminating laser and bond dissociation energy of this pair. This study contributes to a broader understanding of the molecular photoswitching mechanism in SMLM imaging and provides a basis for designing improved photoswitching reagents with potential applications extending to materials science and chemistry. [ABSTRACT FROM AUTHOR]

Ytterbium‐doped lanthanum titanate glasses were prepared by levitation melting for the detailed characterization of the Yb3+${\rm Yb}^{3+}$ spectroscopic properties in the rare‐earth titanate glass host. Low‐temperature fluorescence spectroscopy reveals distinct site‐selectivity in both static and lifetime fluorescence measurements suggesting an absence of clustering as well as significant variation of local ytterbium environments. Typical site‐selectivity behavior of a shrinking Stark manifold with lower excitation energy is observed. At 77 K, both the mean emission frequency and the fluorescence lifetime initially increase as the excitation energy decreases from about 11100 to 10750 cm−1${\rm cm}^{-1}$ and then slightly decrease at lower excitation energy. Temperature‐dependent lifetime measurements between 77 and 420 K show a decreasing lifetime with increasing temperature and are well described by a two‐level thermal activation model. The temperature‐dependent fluorescence spectroscopy coupled with a room temperature white light absorption measurement allow the determination of the Stark energy levels of Yb3+${\rm Yb}^{3+}$ in lanthanum titanate glass as well as the calculation of the laser cross‐sections. [ABSTRACT FROM AUTHOR]

Groundwater contamination caused by hydrocarbons is a common issue worldwide. Determining the volume of light non-aqueous phase liquids (LNAPL) that contaminate the subsurface environment is crucial for planning effective groundwater and soil remediation strategies, as well as determining the remediation endpoint. However, accurate approaches for quantifying the LNAPL volume in subsurface environments are scarce. To address this gap, we developed and tested a novel approach to quantify the volume of oil phase filling the soil pores. Our approach involves using a high-resolution technique, the laser induced fluorescence (LIF), to identify the presence of the oil phase, which was then correlated to total petroleum hydrocarbons (TPH) quantifications. For that, first, we obtained an empirical model to estimate the TPH present in the soil using fluorescence intensity and then, we converted the fluorescence intensity data in each log to equivalent TPH values. We used the model block approach, commonly used for ore resource estimation, to compute and discretize the volume of the aquifer contaminated by LNAPL into a set of blocks using the LIF data. Each block was assigned a mean TPH mass, which we used as a proxy for the LNAPL mass in the block. By summing the LNAPL mass in all blocks, we estimated the total LNAPL volume/mass in the investigated site. Our approach provides a simple and effective way to determine the amount of LNAPL contaminating the soil and groundwater, offering a new perspective for investigating hydrocarbon-contaminated sites. [ABSTRACT FROM AUTHOR]

We theoretically investigate the photoelectron angular distribution induced in argon atoms using an XUV+IR two-color scheme, comprising a Ti:sapphire laser pulse and its 13th harmonic. The photoelectron angular distributions (PADs) are computed by directly solving the three-dimensional time-dependent Schrödinger equation (TDSE) within the single active electron approximation. Particular attention is devoted to analyzing the contributing continuum partial waves of the emitted photoelectrons to the formation of the photoelectron angular distribution. We found that the shapes of the obtained angular distributions for both harmonic and sideband peaks are consistent with the predictions of the generalized Fano rule for the absorption and emission of photons. Moreover, the structure of the energy spectrum of the ejected photoelectrons is presented and discussed where we can remark that the sideband SB + 1 peak is slightly higher than the sideband peak SB − 1 . [ABSTRACT FROM AUTHOR]

AbstractAccurate models of turbulent buoyant flows are essential for the design of the cooling circuit of nuclear reactors and passive safety systems. However, available models fail to fully capture the physics of turbulent mixing when buoyancy becomes predominant with respect to momentum. Therefore, high-fidelity experiments of well-controlled fundamental flows are needed to develop and validate more accurate models. We analyze experiments of positive and negative turbulent buoyant jets, both in uniform and stratified environments, with the aim of understanding the thermal hydraulics of turbulent mixing with variable density and providing high-fidelity data for the development and validation of turbulence models. Non-intrusive, simultaneous particle image velocimetry and laser-induced fluorescence measurements were carried out to acquire instantaneous velocity and concentration fields on a vertical section parallel to the axis of a jet in the self-similar region. The refractive index matching method was applied to measure high-resolution buoyant jets with up to 8.6% density difference. These data are free of the typical errors that characterize optical measurements of buoyancy-driven flows (e.g. natural and mixed convection) where the refractive index of the fluid is inhomogeneous throughout the measurement domain. Turbulent statistics and entrainment of buoyant jets in uniform and stratified environments are presented. These data are compared with non-buoyant jets in a uniform environment, as a reference to investigate the effects of buoyancy and stratification on turbulent mixing. The results will be used for the assessment of current turbulence models and as a basis for the development of a new model that captures turbulent mixing. [ABSTRACT FROM AUTHOR]

Digital PCR (dPCR) holds immense potential for precisely detecting nucleic acid markers essential for personalized medicine. However, its broader application is hindered by high consumable costs, complex procedures, and restricted multiplexing capabilities. To address these challenges, an all‐in‐one dPCR system is introduced that eliminates the need for microfabricated chips, offering fully automated operations and enhanced multiplexing capabilities. Using this innovative oscillation‐induced droplet generation technique, OsciDrop, this system supports a comprehensive dPCR workflow, including precise liquid handling, pipette‐based droplet printing, in situ thermocycling, multicolor fluorescence imaging, and machine learning‐driven analysis. The system's reliability is demonstrated by quantifying reference materials and evaluating HER2 copy number variation in breast cancer. Its multiplexing capability is showcased with a quadruplex dPCR assay that detects key EGFR mutations, including 19Del, L858R, and T790M in lung cancer. Moreover, the digital stepwise melting analysis (dSMA) technique is introduced, enabling high‐multiplex profiling of seven major EGFR variants spanning 35 subtypes. This innovative dPCR system presents a cost‐effective and versatile alternative, overcoming existing limitations and paving the way for transformative advances in precision diagnostics. [ABSTRACT FROM AUTHOR]

This paper delves into the methodology employed in examining lean premixed turbulent flame fronts extracted from Planar Laser Induced Fluorescence (PLIF) images at elevated pressures. In such flow regimes, the PLIF signal suffers from significant collisional quenching, typically resulting in image data with low signal-to-noise ratio (SNR). This poses severe difficulties for conventional flame front extraction algorithms based on intensity gradients and requires intense user intervention to yield acceptable results. In this work, we propose Convolutional Neural Network (CNN)-based Deep Learning (DL) models as an alternative to problem specific conventional methods. The pretrained DL models were fine-tuned, employing data augmentation, on a small annotated dataset including a variety of conditions between SNR ≈ 1.6 to 2.6 and subsequently evaluated. All DL models significantly outperformed the best-scoring conventional implementation both quantitatively and visually, while having similar inference times. IoU-scores and Recall values were found to be up to a factor ≈ 1.2 and ≈ 2.5 higher, respectively, with ≈ 1.15 times improved Precision. Small-scale structures were captured much better with fewer erroneous predictions, becoming particularly pronounced for the lower SNR data investigated. Moreover, by applying artificially modeled noise, it was shown that the range of image conditions in terms of SNR that can be reliably processed extends well beyond the images included in the training data, and satisfactory segmentation performances were found for SNR as low as ≈ 1.1. The presented DL-based flame front detection algorithm marks a methodology with significantly increased detection performance, while a similar computational effort for inference is achieved and the need for user-based parameter tuning is eliminated. It enables a very accurate extraction of instantaneous flame fronts in large image datasets where supervised processing is infeasible, unlocking unprecedented possibilities for the study of flame dynamics and instability mechanisms at industry-relevant conditions. [ABSTRACT FROM AUTHOR]

The process of Infrared Multiphoton Dissociation (IRMPD) was studied in a mixture of vinyl bromide/chlorodifluoromethane (VBr, C2H3Br/CF2HCl) using single and double infrared pulsed transverse excitations atmospheric CO2 laser beams. The dissociation of VBr was investigated using FTIR, and the product composition was analysed, and various dissociation routes were proposed. The study found that the VBr molecules were more heavily dissociated when exposed to the CF2HCl environment than without it. By using a time-resolved LIF, the kinetics reactions with CF2HCl were explored under pseudo-first-order conditions, and the quenching rate constant for the interaction between CF2HCl and C 2 d 3 Π g was published using the classical Stern–Volmer model. The impact of pulsed laser heating on the generation of C 2 a 3 Π u radicals was also observed. The decrease in the intensity of the C 2 (a 3 Π u) LIF signal was due to faster recombination of the C 2 a 3 Π u radicals, together with a decrease in V - V ′ energy transfer and the pressure oscillations produced by the effect of pulsed laser heating in the irradiated volume and the experimental conditions. [ABSTRACT FROM AUTHOR]

The existence of pathogenic microorganisms is a significant contributor to high morbidity rates in both developed and developing countries. Numerous human diseases have been related to Escherichia coli and Enterococcus faecalis. Fast diagnosis of these bacteria is crucial for limiting the progress of the associated diseases. The current study investigated the potential application of femtosecond laser-induced fluorescence spectroscopy (LIF) in monitoring bacteria. The INSPIRE HF100 laser system, which was pumped by a mode-locked femtosecond Ti: sapphire MAI TAI HP laser, delivered 100 femtosecond laser pulses to the samples. E. coli and E. faecalis were exposed to femtosecond laser pulses, and a spectrometer was used to monitor the fluorescence emission spectra. The measured LIF spectra of the two bacteria showed that E. coli and E. faecalis had fluorescence peaks at 502 and 512.5 nm, respectively. When the excitation wavelength varied from 350 to 400 nm, E. coli and E. faecalis fluorescence peak intensities linearly decreased. Furthermore, the LIF peaks revealed that the full width at half maximum of E. coli is 91.9 nm and that of E. faecalis is 101.3 nm. The current study findings suggest that femtosecond laser-induced fluorescence spectroscopy is a reliable, accurate, and sensitive approach for rapidly and directly identifying pathogenic bacteria. [ABSTRACT FROM AUTHOR]

The behavior of ions in the plasma is an essential component in the process of industrial etching. We studied the motions and energy distribution of argon ions in a inductively coupled plasma (ICP) etching tool, by the method of laser induced fluorescence (LIF). The silicon wafer clamped to a chuck at the bottom of the chamber was biased with a 1 MHz 1–1.2 kV peak-to-peak sinusoidal voltage. The plasma is formed with a 2 MHz ICP coil pulsed at 10 Hz. Sheath thickness was measured at different phases of the bias waveform. The experiment also compared the ion motions with and without wafer bias, as well as different switch-on time of wafer bias. For all cases, ion energy distribution functions and the two-dimensional flow pattern were studied near the center and edge of the wafer. Significant vortex flows were observed near the wafer edge. Experiments in which the wafer was biased in the plasma afterglow resulted in a narrow distribution of ion energy close to the bias voltage at the vicinity of the wafer, and the ion incident angle on the wafer was the smallest. The results were compared to simulations using the Hybrid Plasma Equipment Model code. [ABSTRACT FROM AUTHOR]